Flavohemoglobin detoxifies nitric oxide in aerobic, but not anaerobic, Escherichia coli -: Evidence for a novel inducible anaerobic nitric oxide-scavenging activity

Nitric-oxide dioxygenase (NOD) and reductase (NOR) activities of flavohemoglobin (flavoHb) have been suggested as mechanisms for NO metabolism and detoxification in a variety of microbes. Mechanisms of NO detoxification were tested in Escherichia coli using flavoHb-deficient mutants and overexpressors. flavoHb showed negligible anaerobic NOR activity and afforded no protection to the NO-sensitive aconitase or the growth of anoxic E. coli, whereas the NOD activity and the protection afforded with O-2 were substantial. A NO-inducible, O-2-sensitive, and cyanide-resistant NOR activity efficiently metabolized NO and protected anaerobic cells from NO toxicity independent of the NOR activity of flavoHb. flavol-Hb possesses nitrosoglutathione and nitrite reductase activities that may account for the protection it affords against these agents. NO detoxification by flavoHb occurs most effectively via O-2-dependent NO dioxygenation.